Embodiments of the present specification relate generally to computed tomography (CT), and more particularly to self-calibrating CT detectors, systems and methods for self-calibration.
In an imaging system, such as a computed tomography (CT) imaging system, a fan shaped X-ray beam is emitted towards an object such as a patient or a piece of luggage to image a region of interest in the object. The beam is typically attenuated by the object. Subsequently, the attenuated beam is incident on a CT detector having an array of detector elements. In response to the attenuated beam, the detector elements of the array generate respective electrical signals representative of internal information of the object. These electrical signals are processed by a data processing unit to generate an image representative of the region of interest in the object.
Typically, the array of detector elements is constructed to have a standard response for all detector elements. However, there may be variations among the responses of the detector elements. Numerous other factors such as, but not limited to, geometric parameters of the imaging system, detector gain, shading effects of auxiliary components, such as anti-scatter grids or collimators, of the detectors, may influence the response from the detector elements in different ways. In particular, during usage, and/or over time, detector response may change due to variations in temperature, tube spectrum, and gantry movement. It is desirable to calibrate the CT detector to at least partly compensate for degradation of image quality caused due to variation in detector response.
Typically, a calibration is performed before the shipment of the equipment, at the time of installation of the imaging system by the end user (e.g., hospital radiology staff) or by a field engineer employed by the system manufacturer. Calibration values for some or all of the detector elements are computed from the calibration. Subsequently, the calibration values are applied to the electrical signals generated by the detector elements during operation of the imaging equipment. The calibration may be repeated periodically and/or during imaging system modification or maintenance events to regenerate the calibration values.
However, in current systems, there are no mechanisms to detect and correct the variations that occur “during” the operation. This, combined with the fact that calibrations are often not performed as often as may be needed (due to the time consuming nature of existing calibration techniques) results in less effective calibration values continuing to be used for periods longer than may be desirable.